Optical metasurfaces have been extensively investigated, demonstrating diverse and multiple functionalities with complete control over the transmitted and reflected fields. Most optical metasurfaces are, however, static, with only a few configurations offering (rather limited) electrical control, thereby jeopardizing their application prospects in emerging flat optics technologies. Here, we suggest an approach to realize electrically tunable optical metasurfaces, demonstrating dynamic Fresnel lens focusing. The active Fresnel lens (AFL) exploits the electro-optic Pockels effect in a 300 nm thick lithium niobate layer sandwiched between a continuous thick and a nanostructured gold film serving as electrodes. We fabricate and characterize the AFL, focusing 800−900 nm radiation at a distance of 40 μm, with the focusing efficiency of 15%, and demonstrating the modulation depth of 1.5%, with the driving voltage of ±10 V within the bandwidth of ∼6.4 MHz. We believe that the electro-optic metasurface concept introduced is useful for designing dynamic flat optics components.

Plasmonic metasurfaces, representing arrays of gap-surface plasmon (GSP) resonators and consisting of arrays of metal nanobricks atop thin dielectric layers supported by thick metal films, constitute an important subclass of optical metasurfaces operating in reflection and enabling the realization of numerous, diverse and multiple, functionalities. The available phase variation range is however limited to being $$<\! 2\pi$$ < 2 π , a circumstance that complicates the metasurface design for functionalities requiring slowly varying phases over the whole range of $$2\pi$$ 2 π , e.g., in holographic applications. The available phase range also determines the wavelength bandwidth of metasurfaces operating with linearly polarized fields due to the propagation (size-dependent) nature of the reflection phase. We suggest an approach to extend the phase range and bandwidth limitations in the GSP-based metasurfaces by incorporating a pair of detuned GSP resonators into a metasurface elementary unit cell. With detailed simulations related to those for conventional single-resonator metasurfaces and proof-of-concept experiments, we demonstrate that the detuned-resonator GSP metasurfaces designed for beam steering at $${900}\,\,\hbox {nm}$$ 900 nm wavelength exhibit the extended reflection phase and operation bandwidth. We believe that the considered detuned-resonator GSP metasurfaces can advantageously be exploited in applications requiring the design of arbitrary phase gradients and/or broadband operation with linearly polarized fields.

Research in optical metasurfaces has explosively grown in recent years, primarily due to their ability of exercising complete control over the transmitted and reflected fields. Application prospects in many emerging...

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